1. Field of the Invention
The present invention relates to organic light-emitting devices.
2. Description of the Related Art
Organic light-emitting elements (organic EL elements), which are a type of self-light-emitting device, have received attention for flat panel displays. The organic light-emitting element is of a self-emitting type and does not use a backlight. Accordingly, the organic light-emitting element provides a thinner display. In addition, the organic light-emitting element has a high visibility and a wide color reproduction area. Extensive research has been conducted for a commercial product using organic light-emitting elements. In-car component stereo systems, cellular phones, and the like already use organic light-emitting elements as their display elements.
An organic light-emitting element includes an organic light-emitting substrate including a pair of opposing electrodes composed of an anode and a cathode, and an organic light-emitting layer between the electrodes on a substrate such as a glass plate or a film. The external surface of the organic light-emitting element substrate is provided with a sealing layer. In order to extract light from the organic light-emitting layer to the outside, the electrode through which the light is extracted is made of a transparent material, such as ITO (indium tin oxide). The organic light-emitting element emits light by applying a voltage with an external driving circuit. A light-emitting region is formed by a plurality of such organic light-emitting elements arranged on the surface of a substrate so that many images can be displayed.
It is known that conventional organic light-emitting elements are not resistant to water. If, for example, water enters an organic light-emitting element, a dark spot, from which light is not emitted, may be produced in the organic light-emitting element substrate. Even if such a non-light-emitting region does not occur, the light emitting characteristics may change, which results in reduced luminance. This is disadvantageous since it also reduces lifetime.
In order to prevent water in the atmosphere from penetrating the organic light-emitting element and reducing lifetime, some approaches have been proposed. For example, Japanese Patent No. 3,288,242 discloses that a flat glass plate can be provided as the sealing layer on the external surface of an organic EL substrate with a cationic UV curable resin. Japanese Patent Laid-Open No. 2002-134271 discloses a multilayer barrier structure used as the sealing layer of an organic EL element.
In general, an organic light-emitting device includes a planarizing layer that flattens the unevenness resulting from the formation of thin film transistors (hereinafter referred to as TFTs) or the like. The planarizing layer is made of a polymer that can form a highly flat surface. The organic light-emitting device also includes an element isolation layer that isolates a plurality of organic light-emitting elements from each other. The element isolation layer is typically made of a polymer or an inorganic insulating material. Polymers used for these layers include acrylic resin and polyimide resin, and the inorganic insulating material may be silicon nitride or the like. Such a polymer contains more water than inorganic materials, and the water is liable to be left in the planarizing layer (resin layer) and the element isolation layer. Consequently, the water remaining in the planarizing layer (resin layer) and the element isolation layer degrades the organic compound layer of the organic light-emitting element. Even if the element isolation layer is made of an inorganic insulating material, the water in the planarizing layer (resin layer) may penetrate through a crack in the element isolation layer to degrade the organic compound layer.
The portions of the planarizing layer (resin layer) and element isolation layer disposed around the light emitting region are formed with a large width in the in-plane direction so as to permit variations in the in-plane direction of vapor deposition for forming the organic compound layer, or so as to protect a circuit disposed around the light-emitting region. Since the planarizing layer (resin layer) and the element isolation layer are wider around the light-emitting region, the amount of water remaining in these layers increases. The outer area of the light-emitting region is more seriously affected by the water than the middle area of the light emitting region. Thus, the degradation of the organic light-emitting element is pronounced particularly in the outer area of the light-emitting region.